System for dry extracting/cooling heterogeneous material ashes with control of the air inlet in the combustion chamber

ABSTRACT

The present invention relates to a system for dry extracting and cooling incinerator clinkers, mainly comprising an extraction-cooling unit and means for separating the environment of the combustion chamber from that of said unit. The system is able to reduce the final temperature of the extracted clinkers, without exceeding the air quantity that can be admitted at the entrance to the combustion chamber of the incinerator (FIG.  1 ). When the air flow needed for cooling process exceeds said quantity that can be admitted, the system allows exceeding air to be sent in the most appropriate point of the boiler downstream of the combustion chamber, by suitable control means.

FIELD OF THE INVENTION

The present invention relates to a system and method for dry extracting/cooling heavy ashes coming from the combustion of waste inside of incineration plants.

BACKGROUND OF THE INVENTION

Current systems for extracting heavy ashes coming from the combustion of waste in incinerators provide for the use of wet systems.

Heavy ashes outlet from incinerators are discharged into a water-filled tank located downstream of the last combustion grate. The collection tank has the double function of cooling the ash clinkers and of water seal, thereby preventing the entrance in the boiler of ambient air resucked by the value of depression existing therein, which would disturb the combustion process.

The clinkers thus cooled are removed from the collection tank by scrapers or pushers, causing the reascending of the ash along a slope, and the subsequent discharging thereof in downstream apparatuses.

The use of systems for wet extracting causes remarkable inconveniences to the system on itself and to the surrounding environment. The main drawbacks are related to:

-   -   Irreversible loss of chemical energy and sensible heat contained         in the water-cooled ashes. Once the ashes precipitate in the         collection tank, the combustion processes of unburnt material         present therein stop. Moreover, all the thermal content of the         ashes is transferred to the cooling water.     -   High costs of wet ashes transportation and storage, due to their         higher weight, proportional to the humidity content therein.     -   Consumption of water needed for cooling the clinkers.     -   Need to purify the clinkers-contaminated cooling water, prior to         its discharge in the environment.     -   Difficulty of separating the metallic fractions present in the         wet ash, owing to cohesion phenomena between the ash itself and         the metallic fractions to be recovered.     -   Energy expenditure for moving the cooling water, which requires         continuous additions to limit its thermal rise and recover its         losses.     -   High maintenance costs, due to the high corrosion rate of the         apparatuses and pipelines in which the water flows.

The present invention is based instead on the adoption of systems for dry extracting and cooling said clinkers. The adoption of a system for dry extracting incinerator clinkers poses the problem of controlling the entrance of air (air inlet) in the boiler from the section for discharging heavy ashes downstream of the last combustion grate. In fact, an uncontrolled and oversized entrance of air from said section would entail altering the combustion phenomena in the boiler, with a strong and negative impact on the combustion efficiency, the distribution of the heat flow on exchange surfaces, and the formation of pollutants (NO_(x)) and particulate matter.

Moreover, said clinkers, due to the very nature of the fuel used, are heterogeneous and can contain extraneous bodies of remarkable size; this renders advisable the use of environment separation systems alternative to the typical ones used in other applications (e.g., double-clapet valves), which might be at risk of mechanical blocking at the closing and therefore cause the uncontrolled inlet in the combustion chamber of remarkable quantities of air.

Therefore, the technical problem underlying and solved by the present invention is to provide a system and method for extracting and cooling incinerator clinkers which allow obviating the drawbacks disclosed hereto in connection with the known art.

SUMMARY OF THE INVENTION

The above-mentioned problem is solved by a system according to claim 1 and a method according to claim 11.

Preferred features of the invention at issue are present in the claims depending from the invention itself.

The present invention provides some important advantages, some of which are summarized in the following and will be appreciated in full in the light of the detailed description reported hereinafter. In general terms, important advantages of the invention with respect to the known art are the elimination of all problems related to the use of cooling water, the fact of making easier and more economical the processes of clinkers separation and storage, and the fact of allowing the recovery of the thermal and chemical energy contained in the high-temperature ashes.

In more specific terms, the main advantage of the invention consists in that it allows the dry extracting of the clinkers, providing and adequate, effective and efficient cooling of the same without use of cooling water, by operating an effective control on the air inlet in the combustion chamber to which the extracting system is connected.

This is mainly obtained by the use of separating means internal to the extractor and comprised between the extraction zone and the discharge point. Said separating means cause the entrance in the combustion chamber of a predefined quantity of air useful to the cooling of the clinkers and such as not to influence the combustion process.

According to a preferred and particularly advantageous embodiment, said separation is carried out by the use of a series of movable air locks overhung and hinged to the cover of the extractor in a direction substantially perpendicular to the direction of transport, implementing a sort of labyrinth seal with regard to air, allowing anyhow the passage of clinkers in transit on the belt.

In case the quantity of clinkers extracted is such that the quantity of cooling air required and inlet into the combustion chamber exceeds the minimum percent of combustion air that would negatively influence the combustion efficiency, the present invention equips the extracting system with a device for transferring excess cooling air downstream of the combustion chamber. Said device connects the extractor portion downstream of the separating means to a suitable zone of the boiler downstream of the combustion chamber, and it is sized so as to effect load losses sufficient to render the pressure of the extractor portion to which it is connected equal to or higher than the pressure in the combustion chamber. This feature prevents the danger of combustion fumes passing through the extractor.

According to a preferred embodiment, said device for transferring excess air is constituted by a suitable duct, optionally equipped with a dedusting system and a regulation valve in line.

In some system configurations the extracting function and the cooling one can be entrusted to two distinct conveyors, the first one positioned at the combustion chamber and the second one downstream thereof; the environments of the two conveyors being connected by a hopper for feeding the clinkers from the first belt to the second belt. All of this does not alter the concept at the basis of the present invention, since the environments of the two conveyors form a single environment and therefore a single extracting/cooling unit as described above according to a preferred embodiment.

Upon summarizing the detailed description of preferred embodiments reported hereinafter, the present invention relates to a system for dry extracting and cooling incinerator clinkers, able to reduce the final temperature of the extracted clinkers, without exceeding the air flow that can be admitted at the entrance to the combustion chamber of the incinerator. When the air flow needed for cooling process exceeds said quantity that can be admitted, the system allows exceeding air to be sent in the most appropriate point of the boiler downstream of the combustion chamber, by suitable control means.

The proposed system, upon use, is mainly constituted by the following members:

1. a connection hopper between extractor and incinerator, through which clinkers are discharged on the extractor belt, the latter of the type subject of Patent EP 0 471 055 B1;

2. the above-mentioned extractor/cooler, receiving ash in size and fines, the latter coming from the hoppers underlying the combustion grate; at the loading zone, the pitch of the load-bearing rolls of the conveyor belt is thicker in order to better distribute the load deriving from the impact of the free-falling material; the extracting and transport section is sized so as to facilitate the extracting also of maximum-size clinkers;

3. a system for recovering fines, positioned on the bottom of the extractor and constituted by components resisting to high temperatures;

4. separating means present inside the extractor, to limit the entrance of ambient air in the combustion chamber, forming to this end a separation zone between the combustion chamber and the discharge point of the extractor;

5. means for feeding cooling air inside the extractor, positioned on the side walls of the extractor itself, such as to prevent, in case of overpressure, the outlet of hot gases;

6. optionally, a connecting pipeline or duct for the connection between the extractor portion downstream of the separating means and the point of the boiler downstream of the combustion chamber most suitable for the outlet of the cooling air exceeding the maximum acceptable by the combustion chamber; said pipeline may be equipped with a cyclone dedusting system and a regulation valve in line;

7. optionally, a control logic for the pressure existing upstream and downstream of the extractor section equipped with separating means, through the adjustment of the valve located on the mentioned duct.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages, features and application modes of the present invention will be evident from the following detailed description of some preferred embodiments, shown by way of example and not for limitative purposes. The figures of the enclosed drawings will be referred to, wherein:

-   -   FIG. 1 shows a general layout exemplifying a preferred         embodiment of the invention system, in an operation mode which         provides the entrance in the combustion chamber of all the         cooling air;     -   FIG. 2 shows a general layout exemplifying an embodiment of the         invention system, in an operation mode which provides to send         exceeding cooling air in the boiler downstream of the combustion         chamber;     -   FIG. 3 shows a general layout exemplifying an embodiment of the         invention system, in an operation mode which provides to send         exceeding cooling air in the atmosphere, upon filtering         treatment;     -   FIG. 4 shows a schematic cross-sectional view according to the         line A-A of FIG. 1 ;     -   FIG. 5 shows a detail of FIG. 3 highlighting the section for the         passage of cooling air inside the extractor;     -   FIG. 6 shows a schematic cross-sectional view according to the         line B-B of FIG. 2 ;

DETAILED DESCRIPTION OF THE INVENTION

By firstly referring to FIG. 1, a system for dry extracting/cooling incinerator clinkers is designated as a whole with 1.

For greater illustration clarity, the different components of the system 1 will be described hereinafter by referring to the path followed by the clinkers from the extraction thereof from the combustion chamber, designated with 100, to the disposal thereof.

Immediately downstream of the combustion chamber 100, the system 1 provides an extracting and cooling unit 9, based on a dry extractor mainly made of steel with high thermal resistance. Such extractor 9 is of the kind known on itself and described for example in EP 0 252 967, herein incorporated by means of this reference.

The extractor 9 gathers the heavy ashes which precipitate downwards from a combustion grate 101 of the chamber 100 through a transition hopper 102.

The fines are instead transported on the extractor 9 by collection hoppers 8, arranged at the bottom of the combustion grate 101, the latter ones being equipped with double-clapet valves 5 (or equivalent means), apt to separate the environments upstream and downstream thereto, and being positive-pressure hoppers.

The extractor 9, at the side walls of its own casing 98, has a plurality of entrance holes for the outer cooling air, distribuited in a substantially regular way along the development of the extractor 9 itself and each one designated with 10. Such entrances 10 can be equipped with means for adjusting the flow or can be made active or deactivated. They serve as check valves, i.e. prevent, in case of overpressure in the extractor, the outlet of hot gases in the environment.

Inside the extractor 9, stationary 91 and movable 92 separating means are present, apt to cause a substantial pressure separation of the environments upstream and downstream thereof.

The stationary separating means 91 is preferably constituted by metal baffles, preferably arranged at the transmission head of the extractor 9, in a zone upstream of the clinkers loading point. The means 91, by occupying all the available section between the conveyor belt and the related metal container 98, have the function of preventing air entering the extractor 9 from re-entering in the combustion chamber 100 by passing around the transmission drum 931.

The movable separating means 92 is preferably constituted by air locks overhung and hinged to the cover of the extractor 9, arranged in series along the transport section. The number of air locks is such as to assure a remarkable load loss at the entrance of air resucked from the discharge point of the extractor, so as to let in the combustion chamber a known and predefined maximum quantity of air.

As shown in greater detail in FIG. 4, the air locks 92 are preferably with a pivoting multiple body, i.e. constituted by parallel bands 93 hinged therebetween, so as to accompany the contour of the layer of material travelling on the belt. Said parallel bands 93 may be sized so that those more proximal to the conveyor have greater weight to operate a levelling of the layer upon passage of more compressible material. This function, operated mainly by the air locks more proximal to the combustion chamber 100, make more effective the air seal function of the air locks nearer to the discharge point of the extractor 9.

To guarantee the confinement of clinkers extracted in the transport region, the extractor 9, along all of its length, has metal boards 94 for containing the material. Said containing boards 94 provide a minimum vertical distance from the belt, needed to prevent contact and interference therewith.

When needed, in the gap comprised between belt and metal board 94, brushes 95 of metal or other material resisting to high temperatures can be provided so as to improve the seal and further limit air entrance.

The quantity of ambient air entering through the entrances 10 on the side walls of the extractor can be controlled by making a prefixed passage section. As shown in greated detail in FIG. 4, said entrance section or port may be preferably made by horizontal seal plates 96 connected to the external side of the containing boards 94 and fastened thereto at a determined distance from the fins 97 of the conveyor belt. The presence of said seal plates 96 on both sides of the extractor belt and for all the length of transport assures the entrance of a predetermined quantity of air in the extractor 9 and therefore in the combustion chamber 100, there being known the passage section and the depression value in the combustion chamber 100. Of course, such plates 96 can also involve only a portion of the transport (conveying) section of the belt 9, and in particular only part of the portion downstream of the hopper 102.

Therefore, cooling air is resucked into the extractor 9 for the most part through the entrances 10 (and the section determined by the seal plates 96, when present); and partly it is resucked from the discharge point of the extractor through the labyrinth seal operated by the movable air locks 92.

The clinkers cooling on the belt occurs by ambient air that, resucked in such a way by the depression in the combustion chamber, crosses them in countercurrent. Once heated by effect of the thermal exchange with the latter, the air enters the combustion chamber, re-inletting heat therein.

As previously anticipated, in case the quantity of clinkers to be cooled is such that the cooling air needed exceeds the quantity than can be admitted in the combustion chamber, the invention provides the transfer of exceeding cooling air to a boiler zone downstream of the combustion chamber.

In such a system configuration, and by referring to FIG. 2, the device for transferring exceeding cooling air is constituted by a duct 2, connected to the extractor portion downstream of the separating means, preferably equipped with a cyclone dedusting system 3 and an automatic regulation valve 4 in line.

The boiler zone downstream of the combustion chamber 100 being at a lower pressure with respect to the combustion chamber itself, by connecting said zone with the extractor belt 9 there might take place a passage of combustion fumes from the combustion chamber itself to said extractor. To avoid this situation, the duct 2 is sized so as to effect sufficient load losses along the line, such as to obtain in the portion of extractor connected thereto a pressure value equal to that of the combustion chamber.

For a fine adjustment of this condition, the pressure difference between the extractor portions upstream and downstream of the separating means is constantly monitored by means of suitable sensors 7 and adjusted by means of the actuation of the valve 4 on the duct 2.

By referring to FIG. 3, optionally the duct for expelling exceeding cooling air may have a connection different from the above-described one. In this case, in fact, the air, instead of being sucked by the depression existing in a boiler zone downstream of the combustion chamber, can be sucked by a dedicated fan 22 or equivalent means along the duct 21 equipped with regulation means 40 analogous to the hereto-described ones, and then discharged in the atmosphere upon passing into a dedicated filter 210 arranged upstream of the fan 22.

In these last two system configurations (FIGS. 2 and 3), the air entering the extractor 9, through the discharge point 99 and the side entrances 10, provides to complete the cooling in countercurrent of the clinkers present on the belt portion downstream of the separating means, and is then resucked through the duct 2 into a suitable boiler zone downstream of the combustion chamber 100, by referring to FIG. 2, or sent in the atmosphere by the duct 21 and the fan 22, by referring to FIG. 3.

In addition, as shown also in FIG. 6, the extractor 9 is equipped with a system 981 for recovering the fines positioned on the bottom of the metal container 98, consisting of components resisting to high temperatures.

To avoid fines entrainment by ambient air re-entering from the discharge point 99, it is provided the separate discharge 991 of the fines collected from the recovering system, by double-clapet valve 992 or equivalent system for separating the environments.

The present invention has been so far described referring to preferred embodiments. It is to be meant that other embodiments belonging to the same inventive core may exist, all comprised within the protective scope of the herebelow reported claims. 

1. A system fit for dry extracting and cooling incinerator combustion clinkers, comprising: a dry extracting and cooling unit, based on belt conveyor transport means, adapted to be arranged downstream of a combustion chamber; means for inletting cooling air, adapted to allow a controlled inlet of cooling air at a bed of clinkers transported on said belt conveyor transport means, wherein said cooling air laps in countercurrent the bed of clinkers in direction of the combustion chamber; and control means for controlling quantity of said cooling air that reaches a loading point of the clinkers on said belt conveyor transport means for entrance in the combustion chamber, comprising seal members arranged in sequence along said belt conveyor transport means and substantially facing a clinkers transport portion of the belt conveyor transport means, each seal member developing in a direction substantially orthogonal to a direction of transport, said seal members being adapted to determine a controlled load loss in the flow of cooling air, substantially creating a labyrinth-type seal.
 2. The system according to claim 1, wherein each of said seal members is hinged at a casing of said belt conveyor transport means.
 3. The system according to claim 1 wherein each of said seal members is shaped as an air lock with pivoting multiple bodies.
 4. The system according to claim 3, wherein air lock bodies more proximal to said belt conveyor transport means have greater weight, to level the bed of clinkers upon passage of more compressible material.
 5. The system according to claim 1, wherein said control means comprises at least one further stationary seal member arranged at a transmission head of said belt conveyor transport means upstream of the loading point of the clinkers thereon.
 6. The system according to claim 1 wherein said control means comprises a duct adapted to connect an area of said transport means arranged downstream of said seal members in sequence with a boiler area downstream of the combustion chamber.
 7. The system according to claim 6 , comprising dedusting means arranged at said duct.
 8. The system according to claim 6, comprising airflow regulation means, adapted to regulate the air flow in said duct.
 9. The system according to claim 1, wherein said control means comprises means for discharge in the atmosphere of at least part of the cooling air.
 10. The system according to claim 1, wherein said means for inletting cooling air comprises a plurality of air entrances arranged at a casing of said belt conveyor transport means and associated to an entrance section in the belt conveyor transport means having a substantially labyrinth-like structure.
 11. A method for dry extracting and cooling incinerator combustion clinkers, comprising: loading said clinkers on a dry extraction unit, based on belt conveyor transport means and arranging said clinkers downstream of a combustion chamber; cooling said clinkers by a controlled flow of air fed in countercurrent along said belt conveyor transport means in direction of the combustion chamber; carrying out a quantity control of said cooling air entering the combustion chamber by way of a controlled load loss caused by a labyrinth-type seal obtained through seal members arranged in sequence along said belt conveyor transport means and substantially facing a clinkers transport portion of the belt conveyor transport means , each seal member developing in a direction substantially orthogonal to a direction of transport.
 12. The method according to the-preceding claim 11, wherein carrying out said quality control further comprises allowing a selective connection of an area of said belt conveyor transport means arranged downstream of said seal members in sequence with a boiler area downstream of the combustion chamber.
 13. The method according to claim 12, further comprising regulating air flow fed to said boiler area downstream of the combustion chamber.
 14. The method according to claim 11 , wherein entrance of cooling air is obtained at a casing of said belt conveyor transport means by one or more entrance sections in the belt conveyor transport means having a substantially labyrinth-type structure. 